By the way, Kaladin's comment on Taln and Shalash's mental health makes me wonder: Are the Ten Fools based on the Heralds after they broke the Oathpact? Having 9 immortal, mentally ill people on Roshar for millenia seems like it'd have spawned some stories that could have eventually become stories of the Ten Fools. Taln wouldn't be included in this, but with Vorinism and the number 10, I imagine they'd have created something to oppose his virtues.
Also, I can't remember if this is confirmed or not, but on the topic of the Heralds' mental health, is it at all supernatural? Taln seemed to recover somewhat when Dalinar summoned the perpendicularity at the end of Oathbringer. So, is it just severe PTSD, or something supernatural is involved?
I've tried to make it clear in talking about the books that I separate what has happened to the Heralds and normal mental health. What they're suffering from is in large part supernatural--and has to do with the way souls (or Cognitive Shadows) work in the cosmere. So you are correct. This doesn't mean that some normal treatments wouldn't help them, but their core problem has a huge supernatural component.
And yes, there IS a relationship between the ten fools and the Heralds, though people on Roshar wouldn't be able to point it out.
Is the Heralds' madness related to and/or the same thing as the Fused's madness? The Stormfather mentions that each time one of the Fused is reborn, their mind is further damaged. Is it the same with the Herald? To many rebirths, possibly compounded by the fact that they not only often died each Desolation, but were tortured until the next one?
Yes, these two things are related. (There are some hints in Rhythm of War at how Hoid has avoided a similar fate.)
Note that the torture--and the many rebirths--are a big part of this. But their age is also a factor.
Does this mean that a certain cognitive shadow from the Mistborn series is fated to go insane?
Depends on a lot of factors. But the longer a cognitive shadow exists, the more likely these problems are.
Would this affect the Returned as well? What about those with a lot (like 8,000) breaths since they are not cognitive shadows.
Returned are cognitive shadows. In the Cosmere, there is no way to bring someone back to life, other than normal medical resuscitation, without using a cognitive shadow.
What about Dalinar? I thought he has had textbook PTSD, but the screams he continued to hear turned out to be magic.
Dalinar has a whole host of issues, not easily defined by a single definition. Assume, though, that his mental state is a normal response to, in part, supernatural occurrences.
The different for the Heralds is that they have conditions which could only truly exist in the cosmere, even if some of the manifestations and symptoms are similar to what could happen on Earth.
So is that implying that Hoid is a cognitive shadow, or is that just an effect of being really really old? Also does Vasher know about/how to avoid these effects? Probably an RAFO, but...
Come back to that question in about a month or so.